Eu decidi entrar em contato com o Suporte NVidia para responder a pergunta. Resumindo, a resposta foi não, todos os monitores devem estar executando a mesma resolução para uma configuração NVidia Surround 2D suportada .
Esta é a resposta exata deles:
From the email description, I understand that you would like to know if you can use 2D surround with three monitors out of which two will run on 1920x1080 resolution.
Please be assured that I will do my best to help you further or point you in the right direction.
We would like to inform you that in surround mode, the resolution will be always same across all displays and the lowest resolution is selected from all monitors connected. That means all three monitors will run on 1920x 1080 resolution.